The performances of certain types of MOS transistors, particularly on a structure of semiconductor-on-insulator type, SOI, may be improved by the presence of strain in the channel region.
The operation of a P-channel transistor oriented in the <110> crystal direction is accelerated when its channel region is compressively strained in the gate length direction, that is, the drain-source direction or longitudinal direction. Such a P-channel transistor is further accelerated when its channel region is tensilely strained in the transverse direction. The operation of an N-channel transistor oriented in the <110> crystal direction is accelerated when its channel region is strained with a longitudinal tension, the transverse strain having no noticeable effect. Thus, for N-channel and P-channel transistors, it is desirable to provide opposite longitudinal strain, respectively tensile and compressive.
Methods known to simultaneously form P-channel and N-channel transistors have various disadvantages, they are in particular hardly compatible with the coexistence of different strains for N-channel and P-channel types, in particular in the case of transistors having very small cross and longitudinal dimensions, for example, smaller than 500 nm.
There is a need in the art to overcome all or part of the above-described disadvantages.